Effects of insulin-like growth factor I and interactions with transforming growth factor alpha and LH on proliferation of chicken granulosa cells and production of progesterone in culture

The network regulation mechanism of the effects of heat stress on the production performance and egg quality of Jinding duck was analyzed by miRNA‒mRNA

To explore the differential regulation mechanism of heat stress on the egg production performance and egg quality of Jinding ducks, 200 Jinding ducks (360-day-old) in good health and with similar body weights and a normal appetite were selected and randomly divided into a control (normal temperature [NT]) group (20°C-25°C) and a heat stress (HS) group (32°C-36°C), with 4 replicates in each group and 25 ducks in each replicate. The pretrial period was 1 wk, and the formal trial period was 4 wk. At the end of the 4th wk, 12 duck eggs were collected from each replicate to determine egg quality. Pituitary and ovarian tissues of Jinding ducks were collected, transcriptome sequencing was performed to screen differentially expressed miRNAs and mRNAs related to high temperature and heat stress, and a competitive endogenous RNA regulatory network was constructed. The sequencing data were verified by qRT‒PCR method. The following results were obtained: (1) Compared with the NT group, the HS group had a significantly lower laying rate, total egg weight, average egg weight, total feed intake, and feed intake per duck (P < 0.01), an extremely significantly higher feed-to-egg ratio (P < 0.01), and a higher mortality rate. (2) Compared with the NT group, the HS group had an extremely significantly lower egg weight, egg yolk weight, eggshell weight, and eggshell strength (P < 0.01) and an extremely significantly lower yolk ratio and eggshell thickness (P < 0.01, P < 0.05); however, there was no significant difference in the egg shape index, Haugh unit or protein height (P > 0.05). (3) A total of 1,974 and 1,202 genes were identified in the pituitary and ovary, respectively, and there were 5 significantly differentially expressed miRNAs. The differentially expressed genes were involved in the arginine and proline metabolism pathways, ether lipid metabolism pathway, and drug metabolism-cytochrome P450 pathway, which are speculated to be related to the egg production performance of Jingding ducks under high-temperature heat stress. (4) Novel_221 may target the PRPS1 gene to participate in egg production performance; novel_168 and novel_289 may target PIGW; novel_289 may target Q3MUY2; and novel_289 and novel_208 may target PIGN or genes that may be related to high-temperature heat stress. (5) In pituitary tissue, upregulated novel_141 (center of the network) formed a regulatory network with HSPB1 and HSP30A, and downregulated novel_366 (center of the network) formed a regulatory network with the JIP1 gene. In ovarian tissue, downregulated novel_289 (center of the network) formed a regulatory network with the ZSWM7, ABI3, and K1C23 genes, novel_221 formed a regulatory network with the IGF1, BCL7B, SMC6, APOA4, and FARP2 genes, and upregulated novel_40 formed a regulatory network with the HA1FF10 gene. In summary, heat stress affects the production performance and egg quality of Jinding ducks by regulating the secretion of endocrine-related hormones and the release of neurotransmitters as well as the expression of miRNAs and mRNAs in pituitary and ovarian tissues. The miRNA‒mRNA regulatory network provides a theoretical basis for the molecular mechanism that regulates the stress response in pituitary and ovarian tissues, egg quality, and production performance under heat stress.

Insulin-like growth factor-1 is involved in the deteriorated performance of aged laying hens

The underlying mechanism behind the deteriorated laying performance of aged laying hens remains unclear. In the present study, the laying performance and gene expression along the hypothalamus-pituitary-gonad axis were determined. A total of 300 healthy 90-wk-old ISA hens with similar body weights were classified into three groups according to their laying rate between 90 and 94 wk of age. The experimental groups were the low laying rate (<60%, LLR), high laying rate (>85%, HLR), and intermediate laying rate (60% < laying rate < 85%, MLR) hens. At the end of 94 wk of age, eight hens were randomly selected from each group for tissue collection. The gene expression of hormones and their receptors were determined in the hypothalamus, pituitary, and follicles. The results showed that the serum 17-β-estradiol had no significant difference among the three groups. However, the level of insulin-like growth factor 1 (IGF1) in LLR hens was significantly decreased in the serum, small white follicles (SWF), and dominant follicles (DF, P < 0.05). Within the hypothalamus and small yellow follicles (SYF), the mRNA expression level of estrogen receptor was higher in the MLR group (P < 0.05). Compared with HLR hens, the steroid hormone-synthesis key gene, CYP19A1 was significantly decreased in the SWF of MLR-hens and DF of MLR- and LLR-hens (P < 0.05). The mRNA expression level of IGF1 receptor was higher in the hypothalamus, pituitary, SWF, large white follicles (LWF), SYF, and DF of LLR hens, compared to the HLR hens (P < 0.05). These results suggest that decreased IGF1 in serum and follicles was associated with the decreased egg production of aged laying hens. The present study provides novel insights into the endocrine changes in aged hens having different egg production.

Feeding level is associated with altered liver transcriptome and follicle selection in the hen

Genetic selection for particular traits in domestic animals may have altered the optimal feedback regulation among systems regulating appetite, growth, and reproduction. Broiler breeder chickens have been selected for fast and efficient growth and, unless feed restricted, consume excessively resulting in poor reproductive efficiency. We examined the effect of dietary treatment in full fed (FF) and restricted fed (RF) broiler breeder hens on ovarian responses and on liver morphology and transcriptome associated with reproductive function. Although FF broiler breeder hens had lower egg production (p < 0.01), the total number of ovarian follicles >8 mm (p < 0.01), 6-8 mm (p < 0.03), and 3-5 mm (p < 0.04) were greater in FF hens compared to RF hens. There was a large amount of lipid accumulation in the liver of FF hens and differential gene analysis yielded 120 genes that were differentially expressed >2-fold in response to feeding level (p < 0.01; FDR < 0.05). Elevated T3 may indicate that general metabolism was affected by diet and GHR (p < 0.01) and IGF1 (p < 0.04) mRNA expression were both greater in the liver of FF hens as compared to RF hens. It is likely that selection for increased growth, associated with enhanced activity of the IGF1 system, has altered nutritional coupling of feed intake to follicle development.

Effect of mercury on porcine ovarian granulosa cells in vitro

The objective of this in vitro study was to examine dose-dependent changes in the secretion activity [progesterone (P4) and insulin-like growth factor-I (IGF-I)] of porcine ovarian granulosa cells after experimental mercury (Hg) administration, including its apoptotic potential so as to ascertain the possible involvement of Hg in steroidogenesis. Ovarian granulosa cells were incubated with mercuric chloride [mercury (II) chloride or HgCl2] at the doses 50-250 μg mL(-1) for 18 h and compared with control group without Hg addition. Release of P4 and IGF-I by ovarian granulosa cells was assessed by RIA and apoptosis by TUNEL assay. Observations show that P4 release by granulosa cells was significantly (P < 0.05) inhibited at all the doses, while IGF-I release was not affected at any of the doses used, although a decreasing trend in the release of IGF-I was noted in comparison to control. An increasing trend of apoptosis of granulosa cells was noted, the difference being significant (P < 0.05) only at the dose 130 μg mL(-1) HgCl2, in comparison to control. Obtained data suggest a direct effect of Hg on the release of steroid hormone progesterone but not growth factor IGF-I, and a dose-dependent effect on apoptosis of porcine ovarian granulosa cells. Results indicate the interference of Hg in the pathways of steroidogenesis and apoptosis of porcine ovarian granulosa cells.

Prostaglandin E(2) and insulin-like growth factor I interact to enhance proliferation of theca externa cells from chicken prehierarchical follicles

The interactive effect of insulin-like growth factor I (IGF-I) and prostaglandin E2 (PGE2) on the proliferation of theca externa cells (TECs) was investigated in the prehierarchical small yellow follicles of laying hens. IGF-I manifested a proliferating effect like PGE2 on TECs, but this stimulating effect was restrained by AG1024 (IGF-IR inhibitor), KP372-1 (PKB/AKT inhibitor) or NS398 (COX-2 inhibitor). AG1024, KP372-1 or NS398 abolished IGF-I-stimulated COX-2 expression and PGE2 production. Meanwhile, KP372-1, NS398 or AG1024 depressed the PGE2-stimulated expression of COX-2 and IGF-IR mRNA. Therefore, the IGF-I receptor pathway up-regulates COX-2 expression and PGE2 synthesis via PKB signaling cascade, and then PGE2 stimulates IGF-IR mRNA expression to promote TEC proliferation in an autocrine pattern. Overall, the reciprocal stimulation of intracellular PGE2 and IGF-I may enhance TEC proliferation and facilitate the development of chicken prehierarchical follicles.

Mediation of vertebrate life histories via insulin-like growth factor-1

Life-history traits describe parameters associated with growth, size, survival, and reproduction. Life-history variation is a hallmark of biological diversity, yet researchers commonly observe that one of the major axes of life-history variation after controlling for body size involves trade-offs among growth, reproduction, and longevity. This persistent pattern of covariation among these specific traits has engendered a search for shared mechanisms that could constrain or facilitate production of variation in life-history strategies. Endocrine traits are one candidate mechanism that may underlie the integration of life history and other phenotypic traits. However, the vast majority of this research has been on the effects of steroid hormones such as glucocorticoids and androgens on life-history trade-offs. Here we propose an expansion of the focus on glucocorticoids and gonadal hormones and review the potential role of insulin-like growth factor-1 (IGF-1) in shaping the adaptive integration of multiple life-history traits. IGF-1 is a polypeptide metabolic hormone largely produced by the liver. We summarize a vast array of research demonstrating that IGF-1 levels are susceptible to environmental variation and that IGF-1 can have potent stimulatory effects on somatic growth and reproduction but decrease lifespan. We review the few studies in natural populations that have measured plasma IGF-1 concentrations and its associations with life-history traits or other characteristics of the organism or its environment. We focus on two case studies that found support for the hypothesis that IGF-1 mediates adaptive divergence in suites of life-history traits in response to varying ecological conditions or artificial selection. We also examine what we view as potentially fruitful avenues of research on this topic, which until now has been rarely investigated by evolutionary ecologists. We discuss how IGF-1 may facilitate adaptive plasticity in life-history strategies in response to early environmental conditions and also how selection on loci controlling IGF-1 signaling may mediate population divergence and eventual speciation. After consideration of the interactions among androgens, glucocorticoids, and IGF-1 we suggest that IGF-1 be considered a suitable candidate mechanism for mediating life-history traits. Finally, we discuss what we can learn about IGF-1 from studies in free-ranging animals. The voluminous literature in laboratory and domesticated animals documenting relationships among IGF-1, growth, reproduction, and lifespan demonstrates the potential for a number of new research questions to be asked in free-ranging animals. Examining how IGF-1 mediates life-history traits in free-ranging animals could lead to great insight into the mechanisms that influence life-history variation.

Follicle dynamics and its relation with plasma concentrations of progesterone, luteinizing hormone and estradiol during the egg-laying cycle in ostriches

The aims of this study were (i) to describe the changes in the volume of large ovarian follicles (diameter >3 cm) during the 48 h egg laying cycle in farmed ostriches, and (ii) to quantify factors affecting the volume of the largest measured follicle and the plasma concentrations of progesterone (P(4)) and estradiol-17beta (E(2)beta). In eight egg-producing birds, which all ovulated during the study period, transcutaneous ultrasound scanning and blood sampling was performed at 3 h intervals. The average volume of the total number of visualized large follicles (V(total)), the largest measured follicle (V(F1)), the second largest follicle (V(F2)) and of all follicles smaller than F2 (V(F3-Fn)) were each higher before than after oviposition. V(total), V(F2) and V(F3-Fn) nearly doubled in the 24-h period before oviposition, while V(F1) remained at an equal, rather high level until oviposition. Immediately after oviposition V(total), as well as the volume of the other follicle categories, decreased within 6 h, i.e. around the moment of ovulation. By performing statistical analysis on the basis of linear mixed-effects modelling, we quantified that: (i) V(F1) was 13.2% higher before than after oviposition and increased with 6.5% when LH increased with 1 ng/ml; (ii) P(4) levels were 93.2% higher before than after oviposition and increased with 43.1% for every 3 h closer to oviposition; when LH and E(2)beta levels and V(F1) increased with 1 ng/ml, 10 pg/ml and 10 ml, respectively, P(4) increased with 116.6%, 50% and 6.1%; and (iii) E(2)beta levels were 35.6% higher before than after oviposition, increased with 2.7% for every 3 h closer to oviposition and increased with 14.6% when LH increased with 1 ng/ml. It is concluded that during the egg-laying cycle in ostriches: (i) follicular mass, as estimated by the volume of visualized follicles larger than 3 cm, increases before and decreases after ovulation, and (ii) follicular dynamics and its accompanying endocrine plasma hormone profiles during the egg-laying cycle in ostriches follow a pattern similar to that in chickens.

Intra-ovarian growth factors regulating ovarian function in avian species: a review

There is now overwhelming evidence that the avian ovary is a site of production and action of several growth factors that have also been implicated in the functioning of the mammalian ovary. Several members of the Insulin-like growth factor family (IGF), the Epidermal growth factor family (EGF), the Transforming growth factor-beta family (TGF-beta), Fibroblast growth factors (FGF), the Tumour necrosis factor-alpha (TNF-alpha), and others, have been identified either in the granulosa and/or theca compartments of ovarian follicles and in the embryonic and juvenile ovary. Some have been specifically localized to the germinal disc area containing the oocyte. The mRNAs and proteins of the growth factors, receptor proteins and binding proteins of some of the members of each group have been reported in the chicken, turkey, quail and duck. The intra-ovarian roles reported for the different growth factors include regulation of cell proliferation, steroidogenesis, follicle selection, modulation of gonadotrophin action, control of ovulation rate, cell differentiation, production of growth factors, etc. The aim of this paper is to provide a review of the current knowledge of avian ovarian growth factors and their biological activity in the ovary. The review covers the detection of the growth factor proteins, the receptor proteins, binding proteins, their spatial and temporal distribution in embryonic, juvenile and adult ovaries and their regulation. The paper also discusses their roles in each follicular compartment during follicular development. Greater emphasis is given to the major growth factors that have been studied to greater detail and others are discussed very briefly.

IGF-1 receptor signaling pathways and effects of AMPK activation on IGF-1-induced progesterone secretion in hen granulosa cells

IGF-1 plays a key role in the proliferation and differentiation of granulosa cells. However, the molecular mechanism of IGF-1 action in avian granulosa cells during follicle maturation is unclear. Here, we first studied IGF-1 receptor (IGF-1R) expression, IGF-1-induced progesterone production and some IGF-1R signaling pathways in granulosa cells from different follicles. IGF-1R (mRNA and protein) was higher in fresh or cultured granulosa cells from the largest follicles (F1 or F2) than in those from smaller follicles (F3 or F4). In vitro, IGF-1 treatment (10(-8)M, 36h) increased progesterone secretion by four-fold in mixed F3 and F4 (F3/4) granulosa cells and by 1.5-fold in F1 granulosa cells. IGF-1 (10(-8)M, 30min)-induced increases in tyrosine phosphorylation of IGF-1R beta subunit and phosphorylation of ERK were higher in F1 than in F3/4 granulosa cells. Interestingly, IGF-1 stimulation (10(-8)M, 10min) decreased the level of AMPK Thr172 phosphorylation in F1 and F3/4 granulosa cells. We have recently showed that AMPK (AMP-activated protein kinase) is a protein kinase involved in the steroidogenesis in chicken granulosa cells. We then studied the effects of AMPK activation by AICAR (5-aminoimidazole-4-carboxamide ribonucleoside), an activator of AMPK, on IGF-1-induced progesterone secretion by F3/4 and F1 granulosa cells. AICAR treatment (1mM, 36h) increased IGF-1-induced progesterone secretion, StAR protein levels and decreased ERK phosphorylation in F1 granulosa cells. Opposite data were observed in F3/4 granulosa cells. Adenovirus-mediated expression of dominant negative AMPK totally reversed the effects of AICAR on IGF-1-induced progesterone secretion, StAR protein production and ERK phosphorylation in both F3/4 and F1 granulosa cells. Thus, a variation of energy metabolism through AMPK activation could modulate differently IGF-1-induced progesterone production in F1 and F3/4 granulosa cells.

The role of ghrelin and some intracellular mechanisms in controlling the secretory activity of chicken ovarian cells

The general aim of these in-vitro experiments was to determine whether ghrelin controls the secretory activity of chicken ovarian cells and whether its action is mediated by TK-, MAPK-, CDK- or PKA-dependent intracellular mechanisms. We postulated that particular protein kinases could be considered as mediators of ghrelin action (a) if they are controlled by ghrelin, and (b) if blockers of these kinases modify the action of ghrelin. In our in-vitro experiments we investigated whether ghrelin altered the accumulation of TK, MAPK, CDK and PKA in chicken ovarian cells and whether ghrelin, with or without blockers of MAPK, CDK and PKA, affected the secretion of progesterone (P4), testosterone (T), estradiol (E2) or arginine-vasotocin (AVT). In the first series of experiments, the influence of a ghrelin 1-18 analogue (1, 10 or 100 ng/mL) was studied on the expression of TK, MAPK and PKA in cultured chicken ovarian granulosa cells. The percentage of cells containing TK/phosphotyrosine MAPK/ERK1, 2 and PKA was determined using immunocytochemistry. Ghrelin increased the expression of both TK and MAPK. The low concentration of ghrelin (1 ng/mL) increased the accumulation of PKA in ovarian cells whilst the high concentration (100 ng/mL) decreased it. The 10 ng/mL concentration had no effect. In the second series of experiments, the effects of the ghrelin analogue combined with an MAPK blocker (PD98059; 100 ng/mL), a CDK blocker (olomoucine; 1 microg/mL), or a PKA blocker (KT5720; 100 ng/mL), were tested for their effects on the secretion of hormones by cultured fragments of chicken ovarian follicular wall. P4, T, E2 and AVT secretions were measured using RIA and EIA. Ghrelin increased T and decreased E2, but did not affect P4 or AVT secretion. The PKA blocker promoted P4 secretion and suppressed E2 and AVT, but did not affect T secretion. It prevented or even reversed the effect of ghrelin on T and E2, but did not modify its effect on AVT secretion. The MAPK blocker enhanced P4 and T and reduced AVT, but did not affect E2 secretion. It was able to prevent or reverse the effect of ghrelin on T and E, and it induced a stimulatory effect of ghrelin on AVT secretion. The CDK blocker reduced the secretion of AVT, but had no effect on steroid hormone secretion. It induced the stimulatory influence of ghrelin on the secretion of P4 and AVT, but did not modify the effect of ghrelin on other hormones. These observations clearly demonstrate that ghrelin is a potent regulator of the secretory activity of ovarian cells and of TK, MAPK and PKA. Furthermore, they suggest that MAPK-, CDK- and PKA-dependent intracellular mechanisms are involved in the control of ovarian secretion and that they mediate the effects of ghrelin on these processes.

Novel expression and functional role of ghrelin in chicken ovary

Ghrelin has recently emerged as pleiotropic regulator of a wide array of endocrine and non-endocrine functions. The former likely includes the control of gonadal function, as expression of ghrelin and its putative receptor, the GH secretagogue receptor type 1a (GHS-R1a), has been described in mammalian gonads, and direct effects of ghrelin in the control of testicular secretion and cell proliferation have been reported. Yet, the expression and/or functional role of ghrelin in gonads from non-mammalian species remain to be analyzed. The present study aimed to evaluate the expression of ghrelin and GHS-R genes in the chicken ovary, and to assess the potential involvement of ghrelin in the direct control of chick ovarian function. To this end, RT-PCR assays for ghrelin and GHS-R1a mRNAs were performed in ovarian tissue, and cultures of chicken ovarian cells were conducted in the presence of increasing doses (1, 10 or 100 ng/ml) of the ghrelin analog, ghrelin 1-18. Our results demonstrate that both ghrelin and GHS-R1a mRNAs are expressed in chick ovarian tissue. Moreover, challenge of ovarian granulosa cells with ghrelin 1-18 was able to induce markers of proliferation (i.e. expression of both PCNA and cyclin), and to modulate markers of apoptosis (i.e. decreased expression of caspase-3, bax, bcl-2 and TUNEL-positive cells). Moreover, ghrelin 1-18 increased the expression of PCNA, cyclin, bax and p53 in cultures of ovarian follicular fragments, where it also stimulated the release of progesterone, estradiol, arginine-vasotocin (AVT) and IGF-I, but not of testosterone. In conclusion, our study provides novel evidence for the gonadal expression of the genes encoding ghrelin and its cognate receptor in a non-mammalian species, i.e. the chicken ovary, and unravels the potential involvement of this newly discovered molecule in the control of key gonadal functions in the chick, such as proliferation, apoptosis, and hormone release.

Effects of genotype and feed allowance on plasma luteinizing hormones, follicle-stimulating hormones, progesterone, estradiol levels, follicle differentiation, and egg production rates of broiler breeder hens

The aim of this study was to compare and relate plasma hormone levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone (P4), estradiol (E2), and the in vitro P4 production capacity of the largest yellow (F1) follicle granulosa cells with the laying performance of 2 genotypes (a standard S line and a dwarf cross-experimental E line) maintained under ad libitum (SA, EA) or restricted (SR, ER) feeding regimens. Age-related hormone changes were determined from 4 to 50 wk, hormone changes during the ovulatory cycle were determined during lay, and changes in follicle granulosa cell P4-producing capacity in response to LH with or without growth factors were measured in vitro at different ages. The mean laying rate was similar for SR, EA, and ER but were lower for the SA. Plasma LH and FSH concentrations increased with age in all groups and peaked at puberty. Restricted feeding delayed puberty in both genotypes. Concentrations of E2 and P4 increased after puberty in all groups but delayed in restricted hens. Plasma levels of LH, FSH, P4, and E2 before and after puberty were not correlated with egg-laying performance, but peak E2 levels were. Luteinizing hormone and P4 concentrations during the ovulatory cycle showed differences that may be associated with the different laying performances of the 2 genotypes under ad libitum and restricted feeding. The increase in plasma LH concentration (from basal) during the preovulatory surge was higher in the SR than in the SA but was similar for EA, ER, and SA. The increase in P4 was also higher in SR than in the SA with no difference between EA and ER. In vitro P4 production by granulosa cells in response to LH with insulin-like growth factors, and bone morphogenetic protein-7 was different among the SA, SR, EA, and ER; the EA, SR, and ER had greater responses, and the SA had less response. The presence of insulin-like growth factors and bone morphogenetic protein-7 enhanced LH effects depending on the feeding regimen and age of hen. This finding suggests that differences in laying performances among genotypes fed at different nutritional levels may be partly due to differences in processes associated with follicular maturation modulated by gonadotropins and growth factors. It is concluded that the age at puberty is determined mainly by feed allowance, irrespective of genotype, and that differences in laying performance may be due to a combination of factors that include changes in the levels of gonadotropins or ovarian hormones and growth factors, BW, and the condition of the different genotypes under different feeding allowances.

Insulin Stimulates Proliferation but Not 17β-Estradiol Production in Cultured Chick Embryo Ovarian Cells

The development of the chick embryo gonads is influenced by gonadotropins [follicle-stimulating hormone (FSH), luteinizing hormone, human chorionic gonadotropin (hCG)]. We have previously shown that insulin enhanced the production of androgens in the testis of the newly hatched chicken and increased the proliferation of chick embryo testis cells. In the present paper, we have studied the effect of insulin on embryonic chick embryo ovarian cells and compared them with those of human FSH and hCG. The ovaries of 18-d-old chick embryos were dissociated and cultured for different periods in Dulbecco's modified Eagle's medium in the presence and absence of insulin, human FSH, hCG, and combinations of them. 3H-thymidine incorporation was used as an indicator of cell proliferation; steroids were measured by radioimmunoassay. Results showed that insulin enhanced the proliferation of ovarian cells in a dose- and time-dependent manner. Gonadotropins did not affect significantly the ovarian cell proliferation. Insulin did not change 17beta-estradiol production. The combination of insulin and FSH or insulin and hCG decreased the stimulation of estrogen secretion caused by the addition of the gonadotropins. In some experiments, ovarian cells were cultured with or without insulin, and subpopulations were identified. The results showed that insulin but not human FSH or hCG increased the proliferation of germinal cells after 60 h in culture. Insulin and human FSH did stimulate the other 2 subpopulations. In summary, present results suggest that insulin is an important hormone in the development of the chick embryo ovary.

Opposing actions of TGFβ and MAP kinase signaling in undifferentiated hen granulosa cells

The present studies were conducted to establish interactions between transforming growth factor (TGF)-beta and the epidermal growth factor (EGF) family members, TGFalpha and betacellulin (BTC), relative to proliferation and differentiation of granulosa cells in hen ovarian follicles. Results presented demonstrate expression of TGFbeta isoforms, plus TGFalpha, BTC, and ErbB receptors in prehierarchal follicles, thus establishing the potential for autocrine/paracrine signaling and cross-talk within granulosa cells at the onset of differentiation. Treatment with TGFalpha or BTC increases levels of TGFbeta1 mRNA in undifferentiated granulosa cells, while the selective inhibitor of mitogen activated protein kinase signaling, U0126, reverses these effects. Moreover, TGFbeta1 attenuates c-myc mRNA expression and granulosa cell proliferation, while TGFalpha blocks both these inhibitory effects. Collectively, these data provide evidence that EGF family ligands regulate both the expression and biological actions of TGFbeta1 in hen granulosa cells, and indicate that the timely interaction of these opposing factors is an important modulator of both granulosa cell proliferation and differentiation.

The role of protein kinase A and cyclin-dependent (CDC2) kinase in the control of basal and IGF-II-induced proliferation and secretory activity of chicken ovarian cells

The aim of these experiments was to study the role of protein kinase A (PKA), cyclin-dependent kinase 2 (CDC2) and insulin-like growth factor II (IGF-II) in the control of ovarian function in domestic fowl, as well as the role of PKA and CDC2 in mediating the effects of IGF-II on the ovary. For this purpose, we studied the influence of an inhibitor of PKA (KT5720; 50 ng/ml), a CDC2 blocker (olomoucine; 1 microg/ml), IGF-II (0, 1, 10 or 100 ng/ml) and their combinations on cultured fragments of chicken ovarian follicular wall. Accumulation of PKA and CDC2 and secretion of progesterone (P4), testosterone (T), estradiol (E2) and arginine-vasotocin (AVT) were evaluated by using SDS-PAGE-Western blotting and RIA/EIA. IGF-II addition to culture medium stimulated T, E2 and AVT secretion and inhibited P4 secretion. These changes were associated with an increase in PKA and a decrease in CDC2 accumulation. The PKA blocker KT5720, when given alone, increased accumulation of PKA and secretion of T and E2, but not AVT and inhibited P4 secretion. The PKA blocker also prevented and even reversed the effects of IGF-II on PKA and steroid hormones secretion, but enhanced the action of IGF-II on AVT. The inhibitor of CDC2, olomoucine, when given alone, suppressed the expression of CDC2 and the secretion of P4 and AVT (but not T and E2). When given together with IGF-II, it augmented IGF-II-induced suppression of CDC2 and reversed the effects of IGF-II on P4 (but not on T, E2 or AVT). These observations demonstrate the involvement of PKA, CDC2 and IGF-II in regulating the secretory activity of avian ovarian cells. Our data also suggest the involvement of PKA in the mediation of IGF-II effects on P4, T, E2 and AVT secretion. CDC2 can mediate the effects of IGF-II on ovarian P4 secretion but not on other hormones.

Relationship between egg productivity and insulin-like growth factor-I genotypes in Korean native Ogol chickens

Endocrine factors, such as steroid hormones and growth factors, regulate egg productivity in terms of the quantity of egg production, egg weight, sexual maturity, and the number of small yellow follicles (SYF). Insulin-like growth factors (IGF) are involved in the regulation of ovulation rate and ovarian follicular development in chickens, and a relationship between IGF-I genotype and egg weight has been reported. However, the effect of IGF on egg productivity in Korean Native Ogol chickens (KNOC) has been little studied. Therefore, this study was conducted to identify the relationship among endocrine factors (IGF-I, IGF-II, estradiol, and progesterone), IGF-I genotypes, and egg productivity. Frequencies of IGF-I genotypes (AA, AB, BB) were 17.3, 26.9, and 55.8%, respectively, within a population. When compared with the IGF-I genotypes, the AB genotype had the highest serum levels of estradiol and progesterone at 40 and 30 wk of age, respectively; the highest IGF-II concentration in F1 follicles at 60 wk; and was positively associated with the number of SYF at 60 wk. The results showed that the A allele was associated with a higher IGF-II expression in the follicles and stimulated the development of follicles, indicating a positive association of the A allele with egg production and the number of SYF. Therefore, these results suggest that there is a possibility of IGF-I genotypes acting as a genetic marker for egg productivity of KNOC.

Role of tyrosine kinase- and MAP kinase-dependent intracellular mechanisms in control of ovarian functions in the domestic fowl (Gallus domesticus) and in mediating effects of IGF-II

The aim of our study was to examine the involvement of IGF-II, tyrosine kinases (TK)- and MAP kinases (MAPK)-dependent intracellular mechanisms in the control of ovarian functions in the domestic fowl, as well as the role of these kinases in mediating the IGF-II effect on this process. For this purpose, we studied the influence of IGF-II (0,1,10 or 100 ng/ml), inhibitors of TK (AG1024, 1 microg/ml), MAPK (PD98059, 5 microg/ml), and their combinations, on proliferation (expression of proliferation-related substances PCNA), apoptosis (apoptosis-associated protein bax), TK (phosphotyrosine), MAPK (ERK1,2), cyclin-dependent protein kinase 2 (p34/cdc2) and transcription factor CREB-1, as well as on the release of progesterone (P), testosterone (T), estradiol (E) and arginine-vasotocin (AVT) in cultured fragments of ovarian follicles. The presence of substances within ovarian cells was evaluated by SDS PAGE-Western immunoblotting, and release of the substances was measured by using RIA/EIA of ovarian fragments-conditioned medium. It was found, that the addition of IGF-II to the culture medium (1-100 ng/ml) substantially increased expression of PCNA, MAPK and CREB, and decreased the level of p34/cdc2 and bax, but not TK. Furthermore, exogenous IGF-II inhibited P (at a concentration of 100 ng IGF-II/ml medium), and stimulated T (1,10,100 ng/ml), E (10,100 ng/ml) and AVT (1 ng/ml) release by cultured ovarian cells. Inhibitor of TK, when given alone, increased MAPK and E, inhibited p34/cdc2 and AVT, and did not affect accumulation of TK, P or T. Furthermore, TK blocker prevented effects of IGF-II on T, E and AVT, but not on TK, MAPK, p34/cdc2 and P. MAPK blocker augmented PCNA, MAPK, T and AVT expression, but not P or E, and suppressed expression of p34/cdc2 and bax. Furthermore, MAPK inhibitor, given together with IGF-II, prevented or even reversed the action of IGF-II on PCNA, P, T and AVT, but not on MAPK, p34/cdc2, CREB, bax or E. These observations suggest the involvement of IGF-II, TK and MAPK in the control of proliferation, apoptosis, steroid and peptide hormones by avian ovarian cells, as well as of the involvement of these kinases in mediation of some IGF-II effects on ovarian cells.

BMPs and BMPRs in chicken ovary and effects of BMP-4 and -7 on granulosa cell proliferation and progesterone production in vitro

Bone morphogenetic proteins (BMPs) and their receptors (BMPRs) are now known to have important roles in mammalian ovarian folliculogenesis. This study determined the expression of the mRNA encoding for BMPs and their receptors in the chicken ovary and explored possible roles for them. The expression of the mRNA for BMP-2, -4, -6, -7, and BMPR-IA, -IB, and -II was determined and quantified by a semiquantitative RT-PCR. The mRNAs for all the BMPs and receptors determined were present in both the granulosa (G) and theca (T) cells of the F1, F2, and F3 follicles. All BMP mRNAs increased in G cells with follicular development, whereas only BMP-7 mRNA had this trend in the T cells. BMP-2, -4, and -6 mRNAs in T were similar between follicles. BMPR-IA mRNA was similar in F2G and F3G but lower in F1G. BMPR-IB mRNA was similar in G of all follicles, and BMPR-II mRNA increased with development. In the T, each receptor subtype showed equal distribution between follicles. mRNA levels for BMPR-IB and -II were higher in G than in T, suggesting that the G is a major target for BMPs. BMP-4 and -7 stimulated basal, IGF-I-, and gonadotropin-stimulated progesterone production by cultured G cells, with differential responses between cells from the F1 and F3/4. This suggests involvement in follicular differentiation. BMP-4 and -7 reversed the inhibitory effects of transforming growth factor (TGF)-alpha on basal and gonadotropin-stimulated G cell progesterone production, with greater effect in the F1 than in the F3/4. This effect suggests an important role for BMPs interacting with TGF-alpha in modulating the effects of gonadotropins and IGF-I on follicular differentiation. Finally, BMP-7 stimulated G cell proliferation, but BMP-4 inhibited TGF-alpha+ IGF-I- and/or FSH-stimulated G cell proliferation, suggesting a role in the control of follicular growth during development. These effects of BMP-4 and -7 on the G cell function showed relationships with the expression levels of the BMPs and the BMPR-II.

mRNA expression of components of the IGF system and of GH and insulin receptors in ovaries of broiler breeder hens fed ad libitum or restricted from 4 to 16 weeks of age

An evaluation of the insulin-like growth factors (IGF) system in the ovaries of heavy breeder hens during the growing phase was performed to measure the effect of feed restriction. The transcripts of IGF-I, IGF-II, IGF receptor (IGF-R), two IGF binding proteins (IGFBP-2 and IGFBP-5), GH receptor (GH-R) and insulin receptor (I-R) were measured by RT-PCR at 4, 8, 12 and 16 weeks of age in the ovaries of ad libitum fed and feed restricted hens. The transcripts of all genes screened were detected in all feed regime groups and at all ages sampled. However, no significant overall effects of feed restriction on these transcripts were found despite the marked difference in body growth (200% at 16 weeks of age). Similarly there were no significant age effects except for the expression of GH-R-that showed a decrease after 8 weeks of age (P<0.01). Although feed restriction seems to have a relatively limited effect on the expression of these components of the ovarian IGF system in juveniles, a more detailed determination is necessary to determine possible changes nearer to sexual maturity (16 weeks of age onwards). It is concluded that components of the IGF system, GH or insulin may not be involved in the mechanisms that, through restricted feeding, alter ovarian development and function during growth to enable better reproductive performance during lay.

Mitochondrial transmembrane potential changes support the concept of mitochondrial heterogeneity during apoptosis

Dissipation of mitochondrial membrane potential (DeltaPsi(m)) and release of cytochrome c from mitochondria appear to be key events during apoptosis. The precise relationship (cause or consequence) between both is currently unclear. We previously showed in a model of serum-free cultured granulosa explants that cytochrome c is retained in a subset of respiring mitochondria until late in the apoptotic process. In this study we further investigated the issue of heterogeneity by using the DeltaPsi(m)-sensitive probe CM-H2TMRos in combination with a DNA fluorochrome. Changes of DeltaPsi(m) were assessed qualitatively by epifluorescence microscopy and were quantified using digital imaging microscopy. This approach yielded the following results: (a) CM-H2TMRos staining is a reliable and specific procedure to detect DeltaPsi(m) changes in granulosa cells explants; (b) dissipation of transmembrane potential is an early event during apoptosis preceding nuclear changes but is confined to a subpopulation of mitochondria within an individual cell; (c) in frankly apoptotic cells a few polarized mitochondria can be detected. These findings support the hypothesis that ATP needed for completion of the apoptotic cascade can be generated during apoptosis in a subset of respiring mitochondria and is not necessarily derived from anaerobic glycolysis.

Regulation of steroidogenic acute regulatory protein and luteinizing hormone receptor messenger ribonucleic acid in hen granulosa cells

The regulation of steroidogenic acute regulatory protein (StAR) in vitro by gonadotropins was investigated in granulosa cells from prehierarchal and preovulatory hen follicles. Basal levels of StAR messenger RNA (mRNA) in undifferentiated granulosa cells from prehierarchal (6- to 8-mm) follicles were consistently low, but detectable, and were significantly increased by treatment with 8-bromo-cAMP and FSH (but not LH) within 3-6 h of culture. After 20 h of culture, 8-bromo-cAMP, FSH, and LH each increased StAR mRNA levels above those in control cultured cells, and the delayed response to LH treatment was associated with increased levels of LH receptor (LH-R) mRNA. On the other hand, inhibition of mitogen-activated protein (MAP) kinase signaling, using the MAP kinase kinase inhibitors U0126 and PD98059, in the presence of FSH further increased StAR mRNA and protein levels, LH-R mRNA levels, and progesterone synthesis compared with those in cells cultured with FSH alone. The highest basal expression of StAR mRNA during follicle development was found in granulosa from the largest (F1) preovulatory follicle, with comparatively lower levels in granulosa from less mature (F2 plus F3) preovulatory follicles. Treatment with LH rapidly increased StAR mRNA and protein (but not LH-R mRNA) expression in cultures of F1 granulosa and in combined F2 plus F3 granulosa within 3 h, although the magnitude of stimulation was greater in F2 plus F3 granulosa. Compared with results from granulosa cells from prehierarchal follicles cultured for 20 h, inhibition of MAP kinase signaling in the presence of LH for 1 h failed to further enhance levels of StAR or LH-R expression or progesterone production in F2 plus F3 follicle granulosa compared with the effect of LH treatment alone. These results demonstrate that StAR expression in the hen ovary is up-regulated by gonadotropins at least in part via cAMP signaling. The ability of MAP kinase kinase inhibitors to potentiate gonadotropin-induced StAR and LH-R expression plus progesterone synthesis in prehierarchal follicle granulosa cells in vitro suggests that inhibition of paracrine or autocrine factor-mediated MAP kinase signaling in vivo may be a prerequisite for the full potentiation of granulosa cell steroidogenesis that occurs after recruitment into the preovulatory hierarchy. Finally, these results fail to support a role for MAP kinase signaling in acutely modulating LH-mediated StAR expression or progesterone production in hierarchal follicles, such as occurs during the preovulatory surge of progesterone.

Insulin-like growth factors in the regulation of avian ovarian functions

In the past three decades, overwhelming evidence has accumulated to show that insulin-like growth factor (IGF)-I and -II, their receptors and binding proteins (IGFBP) (the IGF system), have major roles to play in the regulation of ovarian function in mammals. Although studies in birds did not start until 5-6 years ago, the limited information thus far available suggests that the IGFs act as autocrine/paracrine regulators of follicular growth and differentiation, just as observed in mammals. The genes for IGF-I and -II, type-I IGF receptor, IGFBP-2, and IGFBP-5 are expressed in both granulosa and theca cells of the chicken ovary. The mechanisms by which the IGF system controls ovarian function in the avian species are complex and involve interactions with the gonadotrophins (LH and FSH), growth hormone, and even other growth factors. Effects are different between strains and nutritional status.

Corticosterone plasma concentration in male mule ducks: effects of sampling sites, repeated samplings and ACTH injections

1. Changes in plasma corticosterone concentrations according to puncture sites and various challenges including injections of an ACTH agonist (Immediate Synacthen) were investigated in male mule ducks. 2. Lower concentrations were measured in samples drawn by puncture from the occipital sinus than at a wing vein site. 3. Immobilisation and a single intramuscular injection of saline solution (1 ml, 0.9%) had no effect on plasma corticosterone after 15 min. 4. A single intramuscular injection of ACTH (5 microg/kg body weight) produced a rise (P<0.05) in corticosterone. Maximum concentrations were measured after 10 min and, in the absence of further sampling, a return to initial levels was observed by 1 h. 5. On the other hand, repeated bleedings following ACTH challenge maintained higher corticosterone concentrations. 6. A single intramuscular injection of ACTH at doses ranging between 0.625 to 20 microg/kg body weight increased corticosterone concentrations (P<0.05) in a dose-dependent manner, with the responses plateauing at doses of 1.25 microg/kg and higher.

Evaluation of jojoba meal as a potential supplement in the diet of broiler breeder females during laying

1. This study was undertaken to investigate whether jojoba meal can be used as a food supplement during the laying period of chickens. 2. The size of eggs laid were smaller and the overall production rate was lower compared to control birds on food without jojoba meal supplementation. Furthermore, both ovary and oviduct weights were lower in jojoba fed birds. 3. This lowering of egg size and production rate was caused by factors present in jojoba which interfere with follicle growth, yolk deposition, progesterone production and the follicular maturation processes, resulting in the ovulation of smaller follicles and a lower ovulation rate.

Roles of transforming growth factor-alpha and epidermal growth factor in chick limb development

We have examined the distribution of transforming growth factor-alpha (TGF-alpha), epidermal growth factor (EGF), and the chicken EGF receptor (c-erbB), in embryonic chick limbs. Prior to limb budding, TGF-alpha is present in prospective limb-forming mesoderm and in prospective apical ectodermal ridge (AER)-forming ectoderm, but is not detected in non-limb-forming flank mesoderm or ectoderm, nor in presumptive non-AER-forming limb ectoderm, suggesting possible roles in initial limb formation and AER induction. Consistent with this possibility, TGF-alpha is present in the mesoderm of the wing buds of the amelic chick mutants limbless and wingless, which form and bud normally, but is absent from limbless and wingless ectoderm, which fails to form an AER. TGF-alpha and EGF are present in the AER of the developing limb, and TGF-alpha, EGF, and c-erbB are present in the underlying subridge mesoderm, suggesting possible roles in reciprocal AER/subridge mesoderm interactions required for limb outgrowth. We found that exogenous TGF-alpha and EGF can promote the outgrowth of limb mesoderm in the absence of the AER in vitro and can also promote the outgrowth of limbless and wingless wing bud explants. EGF is present in ventral but not dorsal limb ectoderm, suggesting a role for EGF in specification of ventral ectoderm. TGF-alpha and EGF are not detected in the differentiating cartilaginous elements or muscle primordia of the limb, suggesting that cessation of TGF-alpha and EGF expression may be required for cartilage and muscle formation. We have found that exogenous TGF-alpha and EGF inhibit chondrogenesis and myogenesis of limb mesenchyme in vitro. Together these results indicate that signaling through the EGF receptor via endogenous TGF-alpha and EGF may be important for initial limb formation, AER induction, outgrowth of limb mesoderm, and regulation of limb chondrogenic and myogenic differentiation.

The expression of transforming growth factor alpha receptor protein and its activation in chicken ovarian granulosa cells of maturing follicles

Epidermal growth factor (EGF) and transforming growth factor alpha (TGF-alpha) are structurally related growth factors that exert their biological actions by binding to the same cell-surface receptor, EGF receptor. However, in chicken cells, human EGF binds with approximately 100-fold lower affinity than human TGF-alpha. In a previous study, we localized EGF/TGF-alpha receptor immunohistochemically in the granulosa and theca of the developing follicles of laying hens. We have also shown that TGF-alpha binds to cell-surface receptors of the granulosa cells. The present study characterizes the nature of the EGF/TGF-alpha receptor. Immunoprecipitation of receptor proteins from cultured granulosa cells with an anti-EGF receptor antibody (12E) shows the expression of a 170-kDa receptor protein. The expression of the receptor protein decreases with follicular enlargement between the F3 and F1. Incubation of the cells with [125I]TGF-alpha followed by cross-linking with bis(sulphosuccinimidyl)suberate showed that TGF-alpha binds a similar (170 kDa) receptor protein immunoprecipitated with the 12E anti-EGF receptor antibody. The binding of TGF-alpha to granulosa cells caused receptor protein oligomerization, yielding the monomeric (170 kDa) and dimeric (340 kDa) protein forms. Oligomerization seemed to favour the formation of the dimeric rather than the monomeric form. Culturing granulosa cells with luteinizing hormone or follicle-stimulating hormone increased the expression of both monomer and dimer forms of the receptor proteins compared with the control. Western blotting analysis with anti-phosphotyrosine antibody revealed that the lysates of TGF-alpha-stimulated cells express phosphotyrosine-containing receptor proteins of 170 kDa and 340 kDa. The results show that chicken granulosa cells express the 170-kDa EGF/TGF-alpha receptor protein, which dimerizes on binding to TGF-alpha, suggesting that the receptor protein may be involved in the signal transduction of TGF-alpha actions in the chicken granulosa cells.

The phylogeny of the insulin-like growth factors

The insulin-like growth factors are major regulators of growth and development in mammals and their presence in lower vertebrates suggests that they played a similarly fundamental role throughout vertebrate evolution. While originally perceived simply as mediators of growth hormone, on-going research in mammals has revealed several hierarchical layers of complexity in the regulation of ligand bioavailability and signal transduction. Our understanding of the biological role and mechanisms of action of these important growth factors in mammals patently requires further elucidation of the IGF hormone system in the simple model systems that can be found in lower vertebrates and protochordates. This review contrasts our knowledge of the IGF hormone system in mammalian and nonmammalian models through comparison of tissue and developmental distributions and gene structures of IGF system components in different taxa. We also discuss the evolutionary origins of the system components and their possible evolutionary pathways.

Insulin-like growth factors in poultry

A large amount of research, primarily in mammals, has defined to a great extent the pleiotropic effects of the IGF system on growth, development, and intermediary metabolism. Similar elucidations in poultry were hindered to some extent by the absence of native peptides (IGF-I and IGF-II) until their purification, followed by the production of recombinant chicken IGFs. In many ways IGF physiology in birds is similar to that in other species, including but not limited to the fact that IGF-I synthesis is both GH- and GH-independent, and that autocrine-paracrine IGF action is evident. However, it is clear that several unique differences in IGF physiology exist between birds and mammals. For example, more IGF is present in the free form in chickens, and the biological responses to the IGFs is different in several metabolic pathways in birds compared to mammals. To date, no unique IGF-II receptor has been identified in birds. Despite an increasing understanding of the IGFs in aves, several important questions remain to be answered. What is the role of IGF-II in embryo development and posthatch growth? Does an IGF-II receptor entity exist in nonmammalian species? How does nutrition affect IGF-I and IGF-II gene expression, and can this information be used to enhance poultry production? What is the biochemical composition of the IGFBPs, and what are their roles in birds? Can the genetic variation present in poultry be used to positively modify IGF gene expression and physiology? How do the IGFs regulate intermediary metabolism? What is the role of the IGFs in the etiology of several disease states associated with rapid growth in poultry, including tibial dyschondroplasia, obesity, ascites, and spiking mortality syndrome? Answers to these questions are relevant to our understanding of the basic mechanisms of IGF physiology as well as possibly assisting in the amelioration of problems found in modern poultry production.